Color display apparatuses (display apparatuses) such as color TV sets and color monitors typically reproduce colors by subjecting RGB primary colors to additive color mixing. A typical example of a video signal supplied to such display apparatuses is a three-dimensional (e.g. RGB and YCrCb) color video signal (video signal).
In the meanwhile, a display apparatus that subjects not less than four primary colors to the additive color mixing has also been proposed. A video signal supplied to such a display apparatus is typically required to be made up of primary-color signals corresponding to the respective primary colors reproduced by the display apparatus. This type of video signal, however, is not in widespread use, and hence it is necessary to specially generate such a video signal.
For this reason, there are needs for a technology to convert a widely-used video signal made up of three primary-color signals to a video signal made up of multi-primary-color signals corresponding to not less than four primary colors.
According to Japanese Laid-Open Patent Application No. 6-261332/1994 (published on Sep. 16, 1994; Patent Document 1), for instance, a multi-primary-color video signal is obtained in such a manner that, (i) it is identified where an RGB three-primary-color video signal having been supplied locates on a chromaticity diagram, (ii) in accordance with the result of the identification, three primary colors are suitably selected from more than three primary colors, and (iii) a linear combination of the selected primary colors is obtained.
The technology taught by Patent Document 1 can realize relatively precise color reproduction, because parameter coefficients are worked out after spreading RGB colors on the chromaticity diagram. In this technology, however, since the coefficients are not intuitively understandable, the parameters cannot be easily adjusted. This technology is therefore hardly practical.